Peter Zijlstra <pet...@infradead.org> writes:
> On Thu, May 15, 2014 at 03:59:20PM -0700, Ben Segall wrote:
>> task_hot checks exec_start on any runnable task, but if it has been
>> migrated since the it last ran, then exec_start is a clock_task from
>> another cpu. If the old cpu's clock_task was sufficiently far ahead of
>> this cpu's then the task will not be considered for another migration
>> until it has run. Instead reset exec_start whenever a task is migrated,
>> since it is presumably no longer hot anyway.
>>
>> Signed-off-by: Ben Segall <bseg...@google.com>
>> ---
>> kernel/sched/fair.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 28ccf50..9f8dfeb 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -4544,6 +4544,9 @@ migrate_task_rq_fair(struct task_struct *p, int
>> next_cpu)
>> atomic_long_add(se->avg.load_avg_contrib,
>> &cfs_rq->removed_load);
>> }
>> +
>> + /* We have migrated, no longer consider this task hot */
>> + se.exec_start = 0;
>
> se->exec_start compiles loads better
Welp. Indeed it does.
From: Ben Segall <bseg...@google.com>
Date: Thu, 15 May 2014 15:38:10 -0700
Subject: [PATCH] sched: fix exec_start/task_hot on migrated tasks
task_hot checks exec_start on any runnable task, but if it has been
migrated since the it last ran, then exec_start is a clock_task from
another cpu. If the old cpu's clock_task was sufficiently far ahead of
this cpu's then the task will not be considered for another migration
until it has run. Instead reset exec_start whenever a task is migrated,
since it is presumably no longer hot anyway.
Signed-off-by: Ben Segall <bseg...@google.com>
---
kernel/sched/fair.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 28ccf50..dd3fa14 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4544,6 +4544,9 @@ migrate_task_rq_fair(struct task_struct *p, int next_cpu)
atomic_long_add(se->avg.load_avg_contrib,
&cfs_rq->removed_load);
}
+
+ /* We have migrated, no longer consider this task hot */
+ se->exec_start = 0;
}
#endif /* CONFIG_SMP */
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